Project Summary/Abstract The urea cycle is the major pathway for detoxification of ammonia in mammals. Arginase 1 deficiency is thought to be the least common of the urea cycle disorders and results in hyperargininemia. In humans, deficiency of this enzyme is characterized clinically by progressive mental impairment, spasticity, growth retardation, and periodic episodes of hyperammonemia. This proposal is two-fold: 1) to continue to advance gene-based therapies for arginase deficiency utilizing appropriate murine models; viral vectors and genomic correction technology will be applied to examine if animals can be corrected behaviorally and biochemically; and 2) to evaluate an iPSC-derived cell therapy approach with hepatocytes placed on bioactive scaffolds to supply urea cycle function. Preliminary data: Our research group has (amongst other findings): 1) constructed and characterized the arginase 1 knockout mouse; 2) demonstrated long-term survival and rescue with recombinant adeno-associated viral vectors; 3) demonstrated that only low-level ureagenesis is necessary for long-term survival; 4) shown that, using an array of behavioral tests, that treated arginase knockout animals lack nervous system abnormalities and there is no difference in learning or behavior when compared to littermates; 5) shown that peripheral metabolism can result in control of circulating plasma arginine; and 6) loss of arginase gene expression results in abnormalities of intrinsic excitability and the dendritic arbor of neurons. In Aim 1, long-term expression of arginase 2 in muscle by viral vector gene therapy will be performed to examine for biochemical and phenotypic correction in a murine model of arginase deficiency. This approach may avoid neutralizing immune responses in patients with null mutations. In Aim 2, studies will examine if an auxiliary liver grown on scaffolds can supply the minimal urea cycle function necessary to lead to phenotypic correction of hyperargininemia. This approach may be successful for other urea cycle disorders. With successful completion of the proposed studies it is expected that a new therapy with gene and cell replacement will be one step closer for patients afflicted with arginase deficiency.